Worm Breeder's Gazette 14(1): 48 (October 1, 1995)

These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.

The beta subunit of the avermectin sensitive glutamate receptor is expressed on pm4 pharyngeal muscle cells.

David Laughton, George Lunt, Adrian Wolstenholme

School of Biology & Biochemistry University of Bath Bath BA2 7AY U.K.

The recently cloned avermectin receptor consists of a glutamate
sensitive beta subunit and an avermectin sensitive alpha subunit which
when co-expressed in Xenopus oocytes lead to the formation of avermectin
potentiated glutamate gated chloride ion channels(1).  Leon Avery et al
have suggested that this receptor mediates the inhibition of pharyngeal
muscle contraction via the glutamatergic motor neuron M3(2).

Screening of the YAC polytene filter and subsequent cosmids with the 5'
end of the beta subunit localised the gene and controlling 5' sequences
to cosmid C35E8, which maps to chromosome 1.  This cosmid was used as
the template for PCR amplification of a DNA fragment consisting of 1426
bp of 5' sequence before the start methionine, plus sequence encoding
the first 24 amino acids of the subunit.  The fragment was subcloned
into the LacZ expression vector, pPD22.11(3) to form a translational

After worm injections we established 6 stably transformed lines which
all showed the same beta-galactosidase activity.  X-gal staining was
present in the 3 pairs of pm4 pharyngeal muscle cell nuclei.  No other
nuclei consistently stained for X-gal.  We have not looked closely at
the developmental expression of this subunit but we did see pharyngeal
staining in some larval stages (L2/3 onwards) and stained nuclei were
seen in some developing eggs.

These results provide further evidence that the Glu-Cl receptor mediates
the glutamatergic inhibition of pharyngeal muscle via the M3 motor
neuron, and point to inhibition of pharyngeal pumping as a major mode of
action for avermectin.  It must be remembered however that these
experiments have localised the glutamate-binding beta subunit only.  The
avermectin binding alpha subunit may be expressed in a number of
locations , for example body wall muscle, as well as pharyngeal muscle.


We thank Ian Hope for his help with the construction of transgenic worms
and Donna Albertson for helping us in the identification of stained


(1) Cully et al. (1994)  Nature 371: 707-711.
(2) Avery et al. (1995) WBG 13(4): 72-73.
(3) Fire et al. (1990) Gene 93: 189-198.